JPH07152229A - Image forming device - Google Patents

Abstract

PURPOSE:To form a uniform image without causing the unevenness of the image caused by the rise of residual potential even in the case of using a small- diameter photoreceptor drum. CONSTITUTION:The photoreceptor drum 13 is provided with a base substance 30 having conductivity and a photoreceptive film 12 formed on the surface of the base substance 30. The drum 13 is rotated over one rotation in order to form one image. The photoreceptive film 12 is electrostatically charged by corona discharge by a main electrostatic charger 14. The corona current of this corona discharge is adjusted in accordance with the revolving speed of the drum 13 by adjusting the current supplied to the charger 14 by a power source 25. Therefore, the dispersion of the electrostatic charging in every rotation is compensated. Thus, the uniform image without unevenness is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic technique, and more particularly to an image forming apparatus for forming an image by charging and image exposing a single-layer organic photosensitive drum having a small diameter.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic technique has been actively developed as an electrostatic copying apparatus or a printing apparatus. In recent years, in order to reduce the size of the image forming apparatus, an image forming apparatus using a small-diameter photosensitive drum has been proposed.

FIG. 8 is a system diagram of an image forming apparatus 1 using a conventional electrophotographic technique. The image forming apparatus 1 includes a rotatable photosensitive drum 3 having a photosensitive film 2 formed on its surface, a main charger 4 for uniformly applying a predetermined amount of electric charge to the photosensitive film 2, and a photosensitive film 2. An optical device 5 for exposing and forming an electrostatic latent image on the photoconductor film 2, a developing device 6 for developing the electrostatic latent image on the photoconductor film 2, and a photoconductor film 2 are formed. A transfer device 8 for transferring the toner image onto the recording paper 7, a cleaning device 9 having a cleaning blade for removing the toner remaining on the photosensitive drum 3, and an electric charge remaining on the photosensitive drum 3 are removed, A discharge lamp 10 for setting the surface potential of the photosensitive drum 3 to a predetermined uniform potential.
And so on.

According to the image forming apparatus 1, the main charger 4 uniformly applies a predetermined amount of electric charge to the photoconductor film 2, and then the optical device 5 irradiates the photoconductor film 2 with light. An electrostatic latent image is formed on the film 2. Thereafter, the developing device 6 supplies the toner onto the photoconductor film 2 to visualize the electrostatic latent image. The toner image on the photoconductor drum 3 is transferred to the transfer device 8
Is transferred onto the recording paper 7. After the transfer, the toner remaining on the photosensitive drum 3 is removed by the cleaning device 9. Next, the static elimination lamp 10 irradiates the photoconductor film 2 with light, removes the electric charge remaining on the photoconductor film 2, and equalizes the surface potential of the photoconductor film 2 to a predetermined potential. After that, the main charger 4 charges the photosensitive drum 3 again. These series of processes are continuously and repeatedly performed by rotating the photosensitive drum 3 many times with respect to one recording paper 7.

In the prior art, an inorganic material or an organic material is used as a photosensitive material forming the photosensitive film 2. Se-based materials, amorphous Si-based materials, etc. are used as the inorganic materials. In recent years, organic materials are often used in terms of safety and workability. Organic photoreceptors using organic materials are classified into laminated organic photoreceptors and single-layer organic photoreceptors. Among these, the single-layer organic photoconductor is preferable from the viewpoint of ease of production.

[0006]

However, the single-layer organic photoconductor film generally has a high residual potential even after charge elimination. Further, there is a problem that the charge potential at the time of charging becomes low due to the photocarriers remaining in the photosensitive layer showing the high residual potential. Further, there is a problem that the photoconductor film having a good chargeability during the short use time also becomes fatigued as the use time becomes longer, trap sites increase, and the chargeability decreases.

Therefore, when the photoconductor film having such a problem is used in the image forming apparatus using the small-diameter photoconductor drum 3, the following problems occur.

FIG. 9 shows the residual potential after static elimination and the surface potential after charging of the photoconductor film 2 for each revolution when an image is formed on one sheet of recording paper 7 through a multi-pass process. Show. As can be seen from FIG. 9, as the number of turns increases, the residual potential increases, and the surface potential of the photosensitive film 2 decreases accordingly. As a result, the problem of image unevenness occurs.

The present invention has been made in order to solve the above problems, and even when a small-diameter photosensitive drum is used, the unevenness of the image caused by the increase of the residual potential does not occur, and the image is uniform. It is an object of the present invention to provide an image forming apparatus capable of forming various images.

[0010]

An image forming apparatus of the present invention comprises a conductive substrate and a photoconductor film formed on the surface of the substrate, and rotates more than one rotation for one image. A photosensitive member, a charging means arranged near the photosensitive member for charging the photosensitive film by corona discharge, and an exposing means for irradiating the charged photosensitive film with light corresponding to an image. A developing unit arranged downstream of the exposing unit along the rotation direction of the photoconductor member, and a corona current amount due to corona discharge of the charging unit, depending on the number of rotations of the photoconductor member. And adjusting means for adjusting, whereby the above-mentioned object is achieved.

The charging means may be a scorotron charging system, and the adjusting means may be means for adjusting the potential of the scorotron grid of the charging means.

The charging means is of a scorotron charging type, and the opening ratio of the grid of the charging means is variable, and the adjusting means adjusts the opening ratio of the grid of the charging means of the photosensitive member member. It may be a means for adjusting according to the number of rotations.

[0013]

In the image forming apparatus of the present invention, the photoconductor member is provided with a conductive base and a photoconductor film formed on the surface of the base. The photoreceptor member is rotated more than one revolution to form one image. The photoconductor film is charged by corona discharge by the charging means. The corona current of this corona discharge is adjusted by the adjusting means according to the rotation speed of the photoconductor member. Therefore, it is possible to compensate for the variation in charging in each rotation. The charged photoconductor film is exposed by the exposure means to form an electrostatic latent image. The electrostatic latent image on the photoconductor film is developed by developing means. As a result, a uniform image having no unevenness is formed.

[0014]

EXAMPLES Examples of the present invention will be described below.

In the image forming apparatus of this embodiment, each photosensitive drum is rotated N (N is a number larger than 1 and is not limited to an integer) to form one image in each process. A decrease in the surface potential of the photoconductor film due to the residual potential is compensated for every revolution at the time of charging, whereby a high-quality image without image unevenness is formed.

An example of the present invention will be described below in the case of using a positive charging type single-layer organic photoreceptor film as an example.

FIG. 1 shows an image forming apparatus 1 according to an embodiment of the present invention.
It is a systematic diagram which shows the structure of 1. This image forming apparatus 11
As shown in FIG. 1, a rotatable small-diameter photoconductor drum 13 in which a photoconductor film 12 made of a single-layer type organic photoconductor is formed on a surface of a drum base 30 made of a metal material such as aluminum. The main charger 14 that uniformly applies a desired amount of electric charge to the body film 12 and the photoconductor film 12 are exposed to expose the body film 12.
Optical device 1 for generating light for forming an electrostatic latent image thereon
5, a developing device 16 for developing the electrostatic latent image on the photoconductor film 12 with toner, a transfer device 18 for transferring the toner image on the photoconductor drum 13 to the recording paper 17, etc., and after the transfer of the toner image,
A cleaning device 19 for removing the toner remaining on the photoconductor drum 13 and an electric charge remaining on the photoconductor drum 13 are removed to make the potential on the photoconductor film 12 uniform to a predetermined potential. A static elimination lamp 20 and the like are provided.

The main charger 14 employs a scorotron charger, and has a discharge wire 21 for corona discharge, a shield case 22 surrounding the discharge wire 21, and a shield case 22 opening to the photosensitive drum 13 side. And a metal grid 23 provided in the opening.
A power supply 25 for supplying a current required for corona discharge is connected to the discharge wire 21 of the main charger 14.

Generally, the saturated charging potential Vs of the photosensitive film 12 is
However, it is desirable to carry out main charging so as to be in the range of 500 to 1000 V, particularly 700 to 850 V. Therefore, when performing corona discharge, it is desirable to apply a high voltage of 4 to 7 kV to the discharge wire 21 of the main charger 14.

In the present embodiment, one image is formed by rotating the photosensitive drum N times, and corona is generated by corona discharge in the n-th rotation process (n is a natural number not less than the minimum integer greater than or equal to N). The current A _n [μA] is adjusted so as to comply with the following (formula 1).

A _n = A ₁ + A (n-1) (Equation 1) In (Equation 1), A is necessary to compensate for the decrease in the charging ability of the photosensitive film 12 during one rotation. It shows the amount of corona current. The value of A varies depending on the photoconductor film 12 to be used and may be set in advance for each image forming apparatus 11. For example, the chargeability of the photoconductor film 12 may be changed every time the image forming apparatus 11 is started. It is also possible to measure the deterioration characteristic and optimize the set value of A based on the measured value.

As described above, since the corona current is increased for each revolution in accordance with the decrease amount of the surface potential of the photosensitive film 12, the decrease of the surface potential due to the decrease of the charging ability is compensated, and the surface potential at the time of charging is compensated. Is constant.

The amount of corona current can be adjusted, for example, by adjusting the current supplied to the discharge wire 21 from the power supply 25 connected to the discharge wire 21.
When a scorotron charger is used for the main charger 14 as in the present embodiment, a grid 23 is connected to a DC grid power supply 24 for adjusting the scorotron grid potential to a plurality of values to adjust the grid potential. It can also be performed by doing. The case of adjusting the grid potential will be described below.

In this case, the grid potential V _n [V] is adjusted by the grid power source so as to comply with the following (formula 2).

V _n = V ₁ + V (n-1) (Equation 2) In (Equation 2), V is the decrease of the surface potential during N rotations when the compensation of the decrease of the surface potential is not performed. Indicates the amount.

Since the corona current increases as the grid potential increases, the surface potential of the photosensitive film 12 also increases as a result. Therefore, if the grid voltage is set to be higher than the grid potential of the previous revolution for each revolution as in (Equation 2), if the charging ability is constant, the surface potential of each revolution is the same as that of the previous revolution. It becomes higher than the surface potential. In this embodiment, since the grid voltage is increased in every cycle in accordance with the decrease amount of the charging ability of the photoconductor film 12, the decrease of the surface potential due to the decrease of the charging ability is compensated, and as a result, the surface potential becomes constant. become. As a result, a high quality image is formed without causing image unevenness. Further, the above corona current can be adjusted by the following method. In this method, the corona current to the photosensitive drum 13 due to corona discharge is controlled by changing the aperture ratio of the grid 23 in each orbiting process.

In this case, the aperture ratio O of the grid 23 is
_n [%] is adjusted so as to comply with the following (formula 3).

O _n = O ₁ + O (n-1) (Equation 3) In (Equation 3), O is the decrease of the surface potential during N rotations when the compensation of the decrease of the surface potential is not performed. The amount of change in the aperture ratio corresponding to the amount is shown.

The opening ratio of the grid 23 has a correlation with the corona current. The larger the opening ratio of the grid 23, the larger the corona current. Therefore, the photosensitive drum 13 is 1
In order to increase the corona current for each revolution in accordance with the amount of decrease in the charging ability of the photoconductor film 12 during rotation, the grid 2
The aperture ratio of 3 is increased. This compensates for the decrease in charging ability of the photoconductor film 12 and makes the surface potential constant during charging.

The rate of increasing the aperture ratio of the grid 23 for each revolution varies depending on the photoconductor film 12 to be used and is set in advance for each image forming apparatus 11. Alternatively, for example, each time the image forming apparatus 11 is activated, the photoconductor film 12
It is also possible to measure the deterioration characteristic of the charging ability of No. 3 and set the rate of change in the aperture ratio of the grid 23 to an optimum value based on the measured value.

A specific method of adjusting the aperture ratio of the grid 23 will be described below.

FIG. 2 is a diagram showing an image forming apparatus in which the aperture ratio of the grid 23 can be made variable. 3 to 7 show details of the main charger 14 of this embodiment. FIG. 3 is a diagram of the main charger 14 according to the present exemplary embodiment as seen obliquely from above. In FIG. 3, in order to make the configuration of the main charger 14 easy to understand, the shield case 22 and a part of the grid 23 are omitted. FIG. 4 is a view of the main charger 14 of the present embodiment as seen from the vertical direction (direction of arrow A in FIG. 3). Figure 5
FIG. 4 is a view of the main charger 14 of the present embodiment as viewed from the lateral direction (direction of arrow B in FIG. 3). The same components as those of the image forming apparatus 11 of FIG. 1 are designated by the same reference numerals.

In this embodiment, the charger width W of the main charger 14 is
1 is set to 11 mm, and the charger length W2 is set to 220 mm. The distance between the grid 23 and the photosensitive drum 13 is 1.
It is set to 0 mm. Further, the diameter of the photosensitive drum 13 in this embodiment is 30 mm, and in this case, A4R
One sheet of image is formed by the process of about 3.2 rounds with the paper of (297 mm) standard.

As shown in FIGS. 3 to 7, the grid 2
Reference numeral 3 denotes a fixed grid plate 51 fixedly arranged with respect to the shield case 22 between the shield case 22 and the photosensitive drum 24, and is arranged closer to the photosensitive drum 13 than the fixed grid plate 51 and is a rail. It has a movable grid plate 52 that is sandwiched by 53 and moves along the fixed grid plate 51. The fixed grid plate 51 has a plurality of openings 60, and the movable grid plate 52 also has a plurality of openings 61 of the same size as the plurality of openings 60 of the fixed grid plate 51. As shown in FIG. 6, in the present embodiment, the shapes of the plurality of openings 60 of the fixed grid plate 51 and the plurality of openings 60 of the movable grid plate 52 are both parallelograms, and the length of the base m1 thereof is long. And the length h of the photosensitive drum 24 along the rotation direction s are 1.1 mm and 1 respectively.
It is 6.5 mm. Further, the plurality of openings 60 of the fixed grid plate 51 and the plurality of openings 61 of the movable grid plate 52.
The long side m2 is formed so as to extend at an angle θ with respect to the rotation direction s of the photosensitive drum 24. This is so that the discharge wire 21 can uniformly and evenly charge the photoconductor film 12 that is charged through the plurality of openings 60 of the fixed grid plate 51 and the plurality of openings 61 of the movable grid plate 52. Is. The value of θ is 30 degrees in this embodiment. Both the fixed grid plate 51 and the movable grid plate 52 are made of a conductive material, and the surface of the movable grid plate 52 on the photoconductor drum side is insulated. In addition, the movable grid plate 52
Has a gear 55 at one end thereof, and the gear 55 of the movable grid plate 52 meshes with and is in contact with a gear 58 attached to the tip of a shaft 57 of the control motor 42. The control motor 42 controlled by the control circuit 44 rotates the gear 58 meshed with the gear 55 of the movable grid plate 52, and as a result, the movable grid 52 moves toward the arrow C.
Direction or C'direction.

FIG. 6 shows the opening 6 of the fixed grid plate 51.
0 and the opening 61 of the movable grid plate 52 completely overlap each other, and as a result, the opening ratio of the opening of the grid 23 to the opening of the shield case 22 becomes maximum, the fixed grid plate 51 and the movable grid plate 52 The relative positional relationship is shown. In this state, the opening 60 of the fixed grid plate 51 and the opening 61 of the movable grid plate 52 are completely overlapped, and the aperture ratio of the grid 23 is maximum.

In FIG. 7, the movable grid plate 52 is moved in the direction of arrow C from the state of FIG. 6 by the movement of the control motor 42, and as a result, the aperture ratio of the grid 23 becomes smaller than that in the state shown in FIG. The relative positional relationship between the fixed grid plate 51 and the movable grid plate 52 in the case is shown. In this state, the openings 60 of the fixed grid plate 51 and the openings 61 of the movable grid plate 52 partially overlap each other, and the aperture ratio of the grid 23 is smaller than the maximum value.

In this embodiment, the opening ratio of the opening of the grid 23 to the opening of the shield case 22 is 90% at the maximum (state shown in FIG. 6) and 60% at the minimum.
Is. In this range, the control circuit 44 changes the aperture ratio and adjusts the corona current, so that the decrease in the surface potential due to the decrease in the charging ability can be compensated. As the optical device 15 used for image exposure, an optical system including a lens, a reflecting mirror, or the like, or a laser light oscillator or the like is used. The developing device 16 includes a developing roller 16 a that supplies the charged toner of the one-component developer or the two-component developer to the surface of the photoconductor film 12. As the transfer device 18, a corona charger similar to the main charger 14 or a contact type charger is used.

In the present embodiment, the amount of static elimination light of the static elimination lamp 20 on the photoconductor film 12 is preferably 5 LUX · SEC or more, particularly 10 LUX · SEC or more. On the other hand, 200L
If it is UX · SEC or more, deterioration of quality occurs due to light fatigue of the photoconductor film 12. As the static elimination lamp 20, any visible light source such as a halogen lamp, a fluorescent lamp, a cold cathode ray tube, or a neon lamp such as red or green can be used. Alternatively, a monochromatic light source such as an LED (light emitting diode) of red, yellow, green or the like can be used.

The photoconductor film 12 of this embodiment is a positive charging type single layer organic photoconductor film, and is formed by mutually dispersing a binder resin, a charge transport medium and a charge generating substance. As the charge generating substance, any organic photoconductive pigment known per se is used. In particular, phthalocyanine pigments, perylene pigments,
Photoconductive organic pigments such as quinacridone pigments, pyranthrone pigments, disazo pigments and trisazo pigments are used alone or in combination of two or more.

As the charge transport medium, a medium in which a charge transport substance is dispersed in a resin medium is used. As the charge transport material, any hole transport material or electron transport material known per se is used for the purpose of the present invention. Examples of suitable hole transport materials are poly-N-vinylcarbazole, phenanthrene, N-ethylcarbazole, 2,5-diphenyl-1,3,4-oxadiazole, 2,5-bis (4
-Diethylaminophenyl) -1,3,4-oxadiazole, bis-diethylaminophenyl-1,3,6-
Oxadiazole, 4,4'-bis (diethylamino)
-2,2'-dimethyltriphenylmethane, 2,4,5
-Triaminophenylimidazole, 2,5-bis (4
-Diethylaminophenyl) -1,3,4-triazole, 1-phenyl-3- (4-diethylaminostyryl) -5- (4-diethylaminophenyl) -2-pyrazoline, p-diethylaminobenzaldehyde- (diphenylhydrazone), etc. , Or a combination of a plurality of these. 2 examples of suitable electron transport materials
-Nitro-9-fluorenone, 2,7-dinitro-9-
Fluorenone, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone, dinitroanthracene, dinitroacridine, It is used in any one of dinitroanthoquinone and the like, or a combination of a plurality thereof.

Various binder resins, for example, styrene-based polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-
Maleic acid copolymer, acrylic polymer, styrene-acrylic copolymer, styrene-vinyl acetate copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy Examples of various polymers include resins, polycarbonates, polyarylates, polysulfones, diallylphthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, polyether resins, phenol resins, and photocurable resins such as epoxy acrylates and urethane acrylates. To be done. A photoconductive polymer such as poly-N-vinylcarbazole can also be used as the binder resin.

The charge generating substance present in the photoreceptor film 12 is suitably in the range of 0.1 to 50 parts by weight, particularly 0.5 to 30 parts by weight, per 100 parts by weight of the binder resin. It is suitable that the charge transport substance is in the range of 20 to 500 parts by weight, particularly 30 to 200 parts by weight, per 100 parts by weight of the binder resin. The thickness of the photoreceptor film 12 is preferably in the range of 10 to 40 μm, particularly 22 to 32 μm in view of high surface potential, printing durability and sensitivity.

As the conductive drum base 30 of the photosensitive drum 12, an aluminum tube, an aluminum tube subjected to alumite treatment, and a conductive resin substrate are generally used. The organic photoconductor layer as the photoconductor film 12 is formed by using a resin, N, N-dimethylformamide,
An amide-based solvent such as N, N-dimethylacetamide;
Cyclic ethers such as tetrahydrofuran and dioxane; dimethyl sulfoxide; aromatic solvents such as benzene, toluene, xylene; ketones such as methyl ethyl ketone; N-
Methyl-2-pyrrolidone; dissolved in a solvent such as phenol and phenols such as cresol, and the charge-generating substance is dispersed therein to obtain a coating composition. This composition is applied to the conductive drum substrate 30 to form the photoconductor film 12.

The present invention has a remarkable advantage in the case of a positive charging type organic single layer photoreceptor, and the positive charging type also has an advantage that less ozone is generated at the time of main charging. In the case of the positive charging type, it is preferable to use a perylene pigment, an azo pigment or a combination thereof as the charge generating substance, and to use 2,6-dimethyl-2 ′, 6′-di te as the charge transporting substance.
Diphenoquinone derivative such as rt-butyldiphenoquinone, 3,3′-dimethyl-N, N, N ′, N′-tetrakis-4-methylphenyl (1,1′-biphenyl)-
It is preferable to use diamine compounds such as 4,4′-diamine, fluorene compounds and hydrazone compounds.

In the above-mentioned embodiments, the drum-shaped substrate on which the photosensitive film is formed is used as the photosensitive member.
A belt-shaped substrate on which a photosensitive film is formed may be used. Further, in the above embodiment, the image forming apparatus of the present invention is described as an electrostatic copying machine, but the image forming apparatus of the present invention is
Regardless of the electrostatic copying machine, any image forming apparatus that forms an image by an electrophotographic method may be used.

[0046]

As is apparent from the above description, the image forming apparatus of the present invention compensates for the decrease in the charging ability of the photoconductor film, which is the case when a small-diameter photoconductor drum is used. However, since the surface potential does not fluctuate for each revolution of the photosensitive drum, it is possible to uniformly form an image.

[Brief description of drawings]

FIG. 1 is a system diagram of an image forming apparatus 11 according to an exemplary embodiment of the present invention.

FIG. 2 is a system diagram showing an image forming apparatus 11 according to another embodiment of the present invention.

3 is a perspective view showing a main charger 14 of the image forming apparatus shown in FIG.

FIG. 4 is a cross-sectional view of the main charger 14 shown in FIG. 3 when viewed from the vertical direction.

5 is a cross-sectional view of the main charger 14 shown in FIG. 3 when viewed from the lateral direction.

6 is a schematic view showing a grid of the main charger 14 shown in FIG.

7 is a schematic view showing a grid of the main charger 14 shown in FIG.

FIG. 8 is a system diagram of a conventional image forming apparatus 1.

9 is a graph showing the residual potential after static elimination and the surface potential after charging of the photosensitive film 2 for each revolution in the image forming apparatus of FIG.

[Explanation of symbols]

 11 image forming apparatus 12 photoconductor film 13 photoconductor drum 14 main charger 16 developing device 19 cleaning device 20 static elimination lamp 21 discharge wire 22 shield case 23 grid 24 grid power supply 25 power supply 30 drum base

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Yamazato 1-22 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd. (72) Inventor Takuji Terada 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Within Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A photoconductor member comprising a conductive substrate and a photoconductor film formed on the surface of the substrate, the photoconductor member being rotated more than one rotation for one image, and the photoconductor member of the photoconductor member. Charging means arranged in the vicinity to charge the photoconductor film by corona discharge, exposure means for irradiating the charged photoconductor film with light corresponding to an image, and along the rotation direction of the photoconductor member, An image forming apparatus provided with a developing unit arranged on the downstream side of the exposing unit and an adjusting unit for adjusting a corona current amount due to corona discharge of the charging unit according to the rotation speed of the photosensitive member. . 2. The image forming apparatus according to claim 1, wherein the charging unit is of a scorotron charging type, and the adjusting unit is a unit of adjusting a potential of a scorotron grid of the charging unit. 3. The charging means is a scorotron charging type, and the aperture ratio of the grid of the charging means is variable, and the adjusting means controls the aperture ratio of the grid of the charging means,
The image forming apparatus according to claim 1, wherein the image forming apparatus is means for adjusting the number of rotations of the photoconductor member.